chapter1.html

VT100向导

is received and will resume transmission when an XON (DC1) code is received regardless
of the AUTO XON/XOFF feature setting.</P>
<P>When either the buffer empties, the <SPAN CLASS="keyname">NO&nbsp;SCROLL</SPAN> key is pressed again, the terminal
is taken out of SET-UP mode, or <SPAN CLASS="keyname">CTRL</SPAN>-<SPAN CLASS="keyname">Q</SPAN> is pressed, the VT100 will transmit
the XON code to resume transmission from the computer to the terminal.</P>
<P>If the host computer software does not support the XON/XOFF codes, data sent
during buffer full conditions, or when the terminal is in SET-UP mode, may be lost.</P>
<P><STRONG>BITS PER CHARACTER</STRONG><BR>
This feature allows the terminal to transmit and receive either 7- or 8-bit characters.
When set for 8-bit operation, bit 8 is set to a space (or 0) for characters
transmitted and is ignored for all characters received.</P>
<P><STRONG>CHARACTERS PER LINE</STRONG><BR>
The VT100 is capable of displaying either 80 or 132 characters per line. In the 80
character per line mode, the screen is 80 characters wide by 24 lines high. In the
132 character per line mode, the screen is 132 characters wide by 14 lines high
(24 lines if the VT100 is equipped with the Advanced Video Option). In the 132
character per line mode, the displayed lines are physically the same width as in the
80 character per line mode but the characters are more compact.</P>
<P CLASS="note">NOTE: When changing from 80 to 132 character per line mode or vice-versa,
the current contents of the screen are lost.</P>
<P CLASS="note">The use of double-width characters reduces the number of characters per
line by half.</P>
<P><STRONG>CURSOR</STRONG><BR>
The VT100 offers a choice of two cursor representations to indicate the "active
position", or where the next character will be placed on the screen. The cursor may
be displayed as either a blinking underline (_) or a blinking block (<IMG SRC="blocksmall.png" ALT="[]" HEIGHT="15" WIDTH="15">). The cursor
selection may perform an additional function; see the SGR escape sequence definition
in <A HREF="chapter3.html">Chapter&nbsp;3</A>.</P>
<P><STRONG>INTERLACE</STRONG><BR>
This feature is used for high resolution options. To reduce screen flicker the interlace
feature should be turned off if such an option is not installed.</P>
<P><STRONG>KEYCLICK TONE</STRONG><BR>
The keyclick is a tone which is generated every time a code transmitting key is
pressed. The keyclick may be turned on or off to suit the operator's needs. However,
research and experience has shown that an operator is more accurate when
there is an audible feedback from the keyboard.</P>
<P>Like the bell tone, the keyclick volume <EM>is not adjustable</EM>.</P>
<P><STRONG>LINE/LOCAL</STRONG><BR>
The LINE/LOCAL feature allows the operator to easily place the terminal in either
an ON-LINE or a LOCAL (off-line) condition. When the terminal is on-line (the
keyboard ON-LINE indicator is ON) all characters typed on the keyboard are sent
directly to the computer and messages from the computer are displayed on the
screen. In the LOCAL condition (the keyboard LOCAL indicator is ON), the terminal
is electrically disconnected from the computer; messages are not sent to or received
from the computer; and characters typed on the keyboard are echoed on
the screen directly.</P>
<P><STRONG>MARGIN BELL</STRONG><BR>
The margin bell feature is much the same as the bell in a typewriter. If the cursor is
eight characters from the end of the current line while typing, the VT100 sounds a
tone to alert the operator.</P>
<P><STRONG>NEW LINE</STRONG><BR>
The new line feature enables the <SPAN CLASS="keyname">RETURN</SPAN> key on the terminal to function like the
<SPAN CLASS="keyname">RETURN</SPAN> key on an electric typewriter. When the new line feature is enabled,
pressing the <SPAN CLASS="keyname">RETURN</SPAN> key generates the carriage return (CR) and line feed (LF)
codes. When a line feed code is received, the code is interpreted as a carriage
return and line feed.</P>
<P CLASS="note">NOTE: If double line feeds occur consistently, turn this feature off since
the computer is already performing this function automatically.</P>
<P>When the new line feature is disabled, the <SPAN CLASS="keyname">RETURN</SPAN> key generates only the CR
code; an LF code causes the terminal to perform a line feed only.</P>
<P><STRONG>PARITY</STRONG><BR>
Parity, when enabled, checks for correct data transmission. If a transmission error
occurs, the VT100 can detect it and indicate its presence by placing a checkerboard
character (<IMG SRC="checkersmall.png" ALT="[]" HEIGHT="15" WIDTH="12">) on the screen in place of the character with the error. The
parity sense feature determines if the parity is even or odd. When parity is disabled,
no parity bit is transmitted or received.</P>
<P CLASS="note">NOTE: If the parity feature is turned off, the parity sense selection will
be disregarded.</P>
<P><STRONG>PARITY SENSE</STRONG><BR>
The parity sense feature defines which of the two methods of parity checking, odd
or even, is being used by the VT100. If the parity feature is on, the terminal's parity
sense must be matched to the parity the computer is sending. If the parity sense
features do not match, most characters sent to the computer will be rejected even
though the character was received correctly by the VT100. If a parity incompatibility
occurs, the checkerboard character (<IMG SRC="checkersmall.png" ALT="[]" HEIGHT="15" WIDTH="12">) will be shown on the screen
in place of the received character.</P>
<P><STRONG>POWER</STRONG><BR>
During the initial installation, the terminal display must be set to the power line
frequency. In the U.S. this is set to 60 hertz.</P>
<P><STRONG>RECEIVE SPEED</STRONG><BR>
The receive speed must be set to match the computer transmit speed. The VT100
is capable of receiving at any one of the following preselected speeds: 50, 75,
110, 134.5, 150, 200, 300, 600, 1200, 1800, 2000, 2400, 3600, 4800, 9600,
19,200 baud.</P>
<P><STRONG>SCREEN BACKGROUND</STRONG><BR>
The screen background feature of the VT100 allows the operator to determine the
background of the screen. In the normal screen mode, the display contains light
characters on a dark background; in the reverse screen mode, the display contains
dark characters on a light background.</P>
<P><STRONG>SCREEN BRIGHTNESS</STRONG><BR>
Unlike most video terminals, the VT100 does not contain switches or knobs to
adjust screen brightness. Instead, the VT100 electronically controls the screen
brightness. This feature eliminates the high failure rate of mechanical controls and
still allows the operator to select the desired level of brightness for maximum
comfort under varied lighting conditions. This setting may be saved like any other
feature in the terminal.</P>
<P><STRONG>SCROLL</STRONG><BR>
Scrolling the upward or downward movement of existing lines on the screen to
make room for new lines at the bottom or top of the screen. It can be performed in
two ways: jump scroll or smooth scroll. In jump scroll mode, new lines appear on
the screen as fast as the computer sends them to the terminal. At the higher baud
rates, the data is very difficult to read due to the rapid movement of the lines. In
smooth scroll mode, a limit is placed on the speed at which new lines of data may
be sent to the terminal. The movement of lines occurs at a smooth steady rate
allowing the data to be read as it appears on the screen.</P>
<P CLASS="note">NOTE: Smooth scroll mode allows a maximum of six lines of data per second to be added
to the screen. The Auto XON/XOFF feature must be enabled and supported by the host
computer to ensure that data is not lost when smooth scroll mode is enabled.</P>
<P><STRONG>TABS</STRONG><BR>
Just like a typewriter, the VT100 can jump or tab to preselected points on a line.
These tab stops may be individually changed, or totally cleared and then set.</P>
<P><STRONG>TRANSMIT SPEED</STRONG><BR>
Transmit speed must be set to match the computer receive speed. The VT100 is
capable of transmitting at any one of the following preselected transmit speeds:
50, 75, 110, 134.5, 150, 200, 300, 600, 1200, 1800, 2000, 2400, 3600, 4800,
9600, and 19,200 baud.</P>
<P>Transmit speed is independent of receive speed; the terminal may transmit data at
one speed and receive data at a different speed.</P>
<P><STRONG>WRAPAROUND</STRONG><BR>
When this feature is enabled, the 81st or 133rd character (depending upon the
line size selected) inserted on a line is automatically placed in the first character
position of the next line. If the wraparound feature was not enabled, the 81st or
133rd character and all following characters would be overwritten into the last
character position of the current line.</P>
<P CLASS="note">NOTE: The use of double-width characters reduces the number of characters
per line by half.</P>
<P><IMG SRC="keys/bk/3.png" ALT="[3]" HEIGHT="40" WIDTH="40"> (shifted)<BR>
The VT100 contains character sets for the U.S. and the United Kingdom. The
difference between the two character sets is one character, the # or &pound; symbol.
When the standard U.S. character set is selected, the uppercase <SPAN CLASS="keyname">3</SPAN> key on the main
keyboard displays the # character. The &pound; character is displayed when the U.K.
character set is selected.</P>
<H2 ID="S1.4">Part 4 -- Self-Testing the VT100</H2>
<P>A self-test mode is built into the VT100 that automatically, or on command, tests
the condition of the terminal should a fault be suspected. The self-test program
checks the following items:</P>
<UL>
<LI>Advanced Video Memory (if option is installed)</LI>
<LI>Nonvolatile Memory (NVR)</LI>
<LI>Internal Memory</LI>
<LI>Keyboard</LI>
</UL>
<P>This test is performed automatically whenever the terminal is turned on.</P>
<H3 ID="S1.4.1">Self-Test Error Codes</H3>
<P>There are two broad categories of errors: fatal and nonfatal.</P>
<P>Fatal errors cause the terminal to immediately stop all operations. No intelligible
information is displayed on the screen; however, the screen most likely contains a
random pattern of characters. The only error indication (in addition to the random
characters) is a possible error code displayed on the programmable keyboard
LEDs, L1--L4; however, no terminal function, including the lighting of LEDs, is
guaranteed if a fatal error is found.</P>
<P CLASS="note">NOTE: The loopback and EIA modem control tests are not performed
on power-up; they must be invoked separately with the proper escape sequence.
See the programmer's section for further information on these tests.</P>
<P>Nonfatal errors do not halt the terminal processor. Instead, the terminal is forced to
LOCAL mode and an error code character is displayed in the upper-left corner of
the screen.</P>
<P>There are five types of nonfatal errors:</P>
<OL>
<LI>(AVO) Advanced Video Option data RAM</LI>
<LI>(NVR) Nonvolatile data RAM checksum error</LI>
<LI>(KBD) Keyboard missing or malfunction</LI>
<LI>(Data) Data loopback error</LI>
<LI>(EIA) EIA modem control error</LI>
</OL>
<P><A HREF="table1-3.html">Table&nbsp;1-3</A> shows the possible nonfatal error characters that may appear on the
screen and the failure represented by each character.</P>
<H2 ID="S1.5">Part 5 -- What To Do in the Event of a Problem</H2>
<P>If it appears that there is a problem in the terminal, you should initiate the power-up
self-test program. This test will help to determine if the problem lies in your
terminal or in some other part of the computer system. <A HREF="table1-4.html">Table&nbsp;1-4</A> describes the
items an operator can check prior to making a service call.</P>
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